1. Field of the Invention
The present invention relates to an index apparatus for indexing a rotary table to a desired angular position.
2. Description of the Prior Art
A conventional index apparatus is provided with a signal generating circuit including an index plate and a proximity switch for generating a signal each time a rotary table is rotated a unit angle. The rotary table is indexed to a desired angular position in response to the number of the signals generated from the signal generating circuit. However, when the rotary table is desired to stop quickly, it may be caused that the rotary table is stopped at a wrong angular position for the following reason. That is, when the rotational speed of the rotary table is abruptly reduced by applying the brake to a driving motor, a driving shaft connected to the driving motor to rotate the rotary table is twisted due to the inertia of the rotary table and is stored up an energy. The energy causes a vibration phenomenon of a periodic rotational movement of the rotary table in alternate opposite directions.
Therefore, if the vibration occurs at the vicinity of a position where the proximity switch is turned on or off by the index plate, a plurality of signals are generated due to the vibration out of relation to the actual rotation of the rotary table, and the rotary table is indexed to a wrong angular position.